The only seat I found really useable was the seat with armrests that we fitted to the 61 in Brunei; subsequently had the same seat in Dutch 61's; 5 hours of shifting, 45 sectors etc, no problem. I think they were French and there were some issues about certification; but they were great.
I had to fully recline the Chinook seat in the cruise (could hardly see out); the co-pilot's side had such bad vertical bounce that he would have to pee after only 45 minutes in his seat. The 76 seats seemed to vary according to what day they rolled out of the factory - I had an anguished correspondence with Nick which roused the fury of my Engineering Director even though it was nothing to do with him. In the end on the 76 I found that if I kept my lower back pushed hard into the seat back I didn't get backache.
Mind you I've a concrete back - 5 lumber vertebrae welded together after what I thought was one of my better Jetranger landings. I think this injury helped me to get through the remaining 16,000 hours more comfortably, but I wouldn't necessarily recommend it.
The reason your seats are bloody awful and your cockpits bloody noisy is because you don't pay for the aircraft you fly; your passengers fare very slightly better because the beancounters need your passengers to pay for the helicopter. The pilot's needs are a long way down the list of priorities.